Speaker
Mr
Ferran Fernandez Banque
(LLS, Barcelona, Spain)
Description
One of the most known 2D X-ray detectors is the MWPC (Multiwire
Proportional Counter). This is a 2D position sensitive gas detector
based in the proportional chamber. It consists of a frame with
parallel wires which form a plane (anode) sandwiched between two
cathodes planes formed also by parallel wires.
In this job, we describe a complete solution to manufacture anodes
and cathodes for a MWPC. The solution consists of a semiautomatic
winding machine and a soldering method by radiation. This method
allows manufacturing one frame in two hours and with a minimum human
intervention. The machine can work with several types of frames and
a great accuracy in the position of the wires can be achieved.
The idea of making an automatic system of manufacturing arises of
several reasons:
- When we work with a big area (> 200x200 mm2) MWPC and spatial
resolution better than 0.3 mm FWHM in the submilisecond scale, the
frames (anode and cathode) need a high accuracy grade in the
positioning and the stress of the wires. With the traditional method
of soldering (by hand), the accuracy achieved in the positioning was
not good enough for our purpose. For example, with wires separated 1
mm, an error of 0.1 mm in the positioning inserts uncertainties of
20% in the gain. Then, when we work with big area detectors, we
achieve a non-homogeneous behavior.
- When we operate with a MWPC in synchrotron facilities, the aging
is one of the main problems due mainly to the fact that high rate X-
rays induce deposits in the frames wires which need to be repaired or
changed often. The traditional method to manufacture these frames
needs a lot of time and ability. It can take a month to make a set
of two cathodes and one anode. For this reason is necessary to
dispose of an automatic and fast system for the manufacture of these
frames.
- Errors in the stress of the wires necessarily imply an error in
the positioning getting the same effect commented in the previous
section. For this reason it is very important that all the wires had
the same stress and this was as bigger as possible (especially for
small diameter wires 10 m).
- The way of fixing the wires to the frames is to solder with tin.
The weldings's shape in the frames must be smooth in order to avoid
sparks and broken wires due to discharges, reducing drastically the
detector's life. In a set of frames of a big area detector there are
more than 1200 weldings, therefore to weld them at the same time all
it is a great idea.
In this job we present a system with the following advantages:
1. With this system a fast and accurate method of frame manufacture
is achieved. The positioning of the wires improves considerably.
2. The weldings has a smooth shape and avoid the electrostatic
discharges.
3. Any technician could work without many problems. It is not
necessary he/she was an authentic artisan.
Primary author
Dr
J.C. Marti'nez
(Laboratori de Llum de Sincrotró ALBA. Campus UAB, Barcelona)
Co-author
Mr
Ferran Fernandez Banque
(LLS, Barcelona, Spain)
